title: Efficacy of different antimicrobials on inhibition of Listeria monocytogenes growth in laboratory medium and on cold-smoked salmon.
abstract: Listeria monocytogenes is of particular concern in cold-smoked fish products as it can survive curing and cold-smoking, and can subsequently grow from low numbers to potentially hazardous levels during refrigerated storage. The purpose of this study was to (i) quantify the effects of organic acids, nisin, and their combinations on controlling L. monocytogenes growth on cold-smoked salmon at refrigeration temperatures, (ii) identify synergistic interactions of binary combinations of these antimicrobials, and (iii) determine if results from laboratory growth media can predict antimicrobial efficacy on cold-smoked salmon. Strains representing the genetic diversity of L. monocytogenes lineages I and II were grown in brain heart infusion (BHI) broth as well as on the surface of commercially produced wet-cured, cold-smoked salmon slices at 7°C. BHI broth and cold-smoked salmon were supplemented with sodium diacetate (SDA, 0.14% water phase (w.p.)), potassium lactate (PL, 2% w.p.), nisin (NI, 50ppm), and binary combinations of inhibitors at the same levels. Cell densities of L. monocytogenes were measured over time and used to calculate growth parameters, including initial cell density (N0), lag phase (λ), maximum growth rate (μmax), and maximum cell density (Nmax) for each antimicrobial treatment. N0 was significantly lowered by addition of NI with a similar average reduction on salmon (2.02±0.99 log(CFU/g)) and in BHI (1.51±0.83 log(CFU/ml)). Among all antimicrobial treatments, the combination of PL and SDA led to the greatest increase in λ both on salmon (7.1±3.6days) and in BHI (9.7±3.8days) when compared to the controls. The combination of PL and SDA had synergistic effects on increasing λ and lowering Nmax both in BHI and on salmon. Among all the treatments tested, the combination of NI and PL led to the greatest reductions in Nmax on salmon. We observed positive correlations between the growth parameters obtained from BHI broth and cold-smoked salmon, indicating that growth of L. monocytogenes in broth, to some extent, qualitatively reflected characteristics of growth on cold-smoked salmon under antimicrobial stresses. Results from BHI could quantitatively predict the variability of growth parameters obtained from salmon for lineage II strains, but not for lineage I strains. Although results from laboratory growth medium may not provide exact predictions of antimicrobial efficacy on cold-smoked salmon, they could be used to rapidly identify effective combinations for further examination on cold-smoked salmon.
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853, USA. st543@cornell.edu
authors.forename: Silin
authors.initials: S
authors.lastname: Tang
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Stasiewicz
authors.forename: Martin
authors.initials: M
authors.lastname: Wiedmann
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Boor
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Bergholz
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D003080:Cold Temperature; D015169:Colony Count, Microbial; D003470:Culture Media / Q000494:pharmacology*; D005516:Food Microbiology; D005519:Food Preservation / Q000592:standards*; D008089:Listeria monocytogenes / Q000187:drug effects* / Q000254:growth & development; D009561:Nisin / Q000494:pharmacology; D012474:Salmon / Q000382:microbiology*; D012492:Salts / Q000494:pharmacology
chemical_list: D000085:Acetates; D000890:Anti-Infective Agents; D003470:Culture Media; D012492:Salts; D009561:Nisin; C548838:sodium diacetate
keywords: Antimicrobials; BHI; CTRL; Cold-smoked salmon; L. monocytogenes; N(0); N(max); N(maxr); N(r); NI; NIPL; NISDA; Nisin; PL; PLSDA; Potassium lactate; RTE; SDA; Sodium diacetate; T(log); Tukey HSD adjusted p-values; adj. P; brain heart infusion; control; initial cell density; initial cell density reduction; lag phase; maximum cell density; maximum cell density reduction; maximum growth rate; nisin; nisin combined with potassium lactate; nisin combined with sodium diacetate; potassium lactate; potassium lactate combined with sodium diacetate; predicted time for 1 log L. monocytogenes growth; ready-to-eat; sodium diacetate; w.p; water phase; λ; μ(max)